A great variety of electrochemical sensors utilizing an ion-sensitive membrane for the measurement of various ions in solution are known. In general terms, the ion-sensitive membrane contains a compound which interacts with the ions of interest. By the appropriate use of the sensor as an electrode, an electrical effect resulting from the interaction of the ions with the membrane can be measured to provide an indication of the activity of the ions in solution. If the membrane interacts selectively with a particular ion, the sensor may be described as ion-selective rather than ion-sensitive.
Examples of electrochemical sensors include those based on an underlying silicon structure such as microelectronic field effect sensors in which the gate region of the sensor is covered with an ion-sensitive membrane. Such sensors require the precise deposition of an ion-sensitive membrane over a very small surface area.
U.S. Pat. No. 4,352,726 describes the preparation of field effect sensors wherein the ion-sensitive membrane is produced by depositing a polymer containing a macrocyclic ionophore over the surface of the sensor. It specifically describes coating the sensor with an epoxy-type polymer which is subsequently cured for many hours. Superfluous hardened polymer has to be removed by ion etching so that only the gate region of the sensor is covered by the membrane.